Furnace construction



Jan. 13, 1953 H. M. WEIR FURNACE CONSTRUCTION 7 Sheets-Sheet 1 Filed Sept 14. 1949 INVENTOR Hnmcz M.WEIH 2 ATTORNEY Jan. 13, 1953 H. M. WEIR 2,625,140

FURNACE CONSTRUCTION Filed Sept. 14. 1949 7 Sheets-Sheet 5 as f Qnnentor '38 HORACE M.Wzm

(Ittorneg H. M. WEIR FURNACE- CONSTRUCTION Jan. 13, 1953 '7 Sheets-Sheet 4 Filed Sept. 14, 1949 Fig.5

. Invefitor v HORACE M. WEIR (Ittorneg Jan. 13, 1953 H. M. WEIR 2,625,140

FURNACE CONSTRUCTION Filed Sept. 14, 1949 7 Sheets-Sheet 5 Fig.7

INVEIYTOR. 82 HORACE M. WEIR /GQW MM ATTORNEY Jan. 13, 1953 H. M. WEIR FURNACE CONSTRUCTION 7 Sheets-Sheet 6 Filed Sept. 14. 1949 INVEN TOR.

. HORACE M. WEIR ATTORNEY Jan. 13, 1953 Filed Sept. 14. 1949 H. M. WEIR 2,625,140

FURNACE CONSTRUCTION 7 Sheets-Sheet 7 3 INVENTORf HORACE M. WEIR ATTORNEY Patented Jan. 13, 1953 UNITED STATES PATENT OFFICE FURNACE CONSTRUCTION Horace M. Weir, Merion, Pa.

Application September 14, 1949, Serial No. 115,731

12 Claims.

This invention relates to a furnace construction and to a method of heating fluids in tubes by circulating the fluids in two separate series or banks of vertical interconnected tubes, one series of tubes being placed in heat exchange relationship in a furnace combustion zone to expose the tubes to radiant heat and a second series or bank of vertical interconnected tubes positioned in a convection zone where they are in heat exchange relationship with the gases generated in the combustion zone.

One object of my invention is to provide a fluid heating structure in a form readily adapted to be completely prefabricated in the shop and adapted to be erected on the site of use at relatively low cost. Another object of the invention is to provide a compact self-sustaining structure for the purpose of heating fluids and at the same time to ensure that energy latent in the combustible fuel is transferred with high efficiency to the fluid which is to be heated.

My invention is particularly suited for the continuous heating of a stream of petroleum oil and I shall hereinafter refer to oil as the material which is being heated. It should be understood, however, that the furnaces constructed in accordance with my invention are equally well adapted to the heating of any fluid continuously or to the heating of a gas, a mixture of gases or a mixture of gases and liquids. I therefore use the term oil hereinafter merely as a means of simplification in the description and it is to be understood that I am nowise limited thereby to the application of my invention for this fluid only.

According to one embodiment of my invention I provide a furnace construction comprising preferably a vertically arranged substantially cylindrical combustion or radiant chamber which is lined with a refractory or insulating material. The chamber is surmounted by a flue gas stack aligned with the vertical axis of the combustion chamber through which the flue gases escape. A series of closely spaced vertically interconnected heat absorbing tubes are positioned annularly about the inner periphery and adjacent the refractory lining of the combustion chamber so as to be exposed to the radiant heat generated in the combustion chamber. A number of suitable burners for the combustion of fuel oil, gas or powdered fuel are arranged both at the base and top of the combustion chamber for directing burning fuel and the products of combustion thereof in a central longitudinal and unobstructed path through the combustion chamber.

The upper portion of the combustion chamber is surrounded by a concentric annular convection chamber formed by walls of refractory material. A second series of vertically interconnected tubes are positioned within this convection chamber. The refractory lining of the combustion chamber is provided with flue gas openings preferably at the medial zone of the combustion chamber which communicate with the bottom of the convection chamber through which the combustion gases can pass outwardly into the convection chamber. The combustion gases flow upwardly in the convection chamber and then pass upwardly through the stack.

The fluid to be heated to a predetermined temperature is preferably first preheated by circulating it through a series of vertical tubes arranged in the convection chamber in full stream or in divided streams to absorb heat by convection from the combustion gases passing through the convection chamber and then passing the preheated fluid through a series of vertical tubes arranged in the combustion chamber to absorb radiant heat generated by the top and bottom burners in the combustion chamber in a manner which will be fully explained hereinafter.

Further details and advantages of my invention will be apparent from the following description and appended drawings, wherein:

Figure 1 is a plan view of an embodiment of my furnace construction,

Figure 2 is an elevational view of the furnace,

Figure 3 is a vertical sectional view of the furnace taken on lines 3-3 of Figure 4,

Figure 4 is a sectional view taken on lines 4-4 of Figure 3,

Figure 5 is an enlarged vertical sectional view of the upper part of a modified form of the furnace construction,

Figure 6 is a sectional view taken on lines 56 of Figure 5,

Figure '7 is a vertical sectional view of still another modification of my furnace construction,

Figure 8 is an enlarged fragmental vertical sectional view of the bustle pipe shown in Figure '7,

Figure 9 is a sectional view taken on lines 9-9 of Figure 7,

Figures 10 is a sectional view taken on lines Ill-IE3 of Figure 9, and

Figure 11 is a sectional view taken on lines I i-ll of Figure 7.

Referring to Figures '1 to 4, the furnace construction comprises an outer vertically positioned cylindrical metal shell or jacket indicated by numeral I6 formed of a plurality of suitably joined metal plates such as of steel. The shell I is supported by a plurality of vertically positioned structural Ibeam members 8 and 9, as shown in Figure 2. An upper platform 6 is supported by beam members I for providing access to the upper portion of the furnace. A lower platform 3 is supported by beam members 4 for providing access to the lower portion of the furnace. A plurality of openings 2 are provided adjacent the lower end of the shell for peep holes extending into the interior of the furnace. A ladder I is provided for access to a platform adjacent the burners at the bottom of the furnace. Another ladder 5 is provided for access to the upper platform 6. The top II of the cylindrical shell is closed by suitable steel plates attached to the shell I6 which are lined interiorly with refractory material l2. The upper cylindrical portion I4 of the steel shell has a greater diameter than the lower portion I3 of the shell for a purpose which will be explained later. The steel shell It! is lined on its inner face with a refractory or insulating material of suitable thickness whereby the temperature in the com bustion zone is moderated when the furnace is in operation so that the outer steel shell is not ordinarily heated to more than about 200 F.

, at any part thereof. As shown in Figure 3, the

lower portion I3 of the steel shell I0 is lined on its inner surface with a layer of refractory or insulating material 1 5 and with a layer of refractory material l6 at the upper portion I 4 of the steel shell. A refractory or insulating cylindrical wall I! substantially circular in cross-section is provided in the upper portion I4 of the shell I0 and is spaced inwardly of the refractory lining l6 and concentric therewith. The refractory wall I! is supported on plates I9 resting on brackets attached to the shell Ill. The inner refractory wall (I forms an annular space or chamber I8 at the upper portion of the furnace through which the combustion gases generated in the furnace are adapted to flow and then pass out to the furnace stack. The upper steel shell and refractory lining are provided with suitable peep holes 21 to the interior of the convection chamber I8.

The top cover plate II is lined. on its inner face with a refractory lining 22, as shown in Figure 3. The top cover plate I I is provided with openings adjacent its outer periphery to permit sections 22' of the refractory lining to be removed for affording access to the convection chamber l8 and also the combustion chamber for removing the tubes 30 and tubes 26 when repairs are required. The inner cylindrical combustion zone is closed at the top by means of a ceramic or refractory cover 23 suitably supported by steel structural member 24. Removable sections 24' may be provided at the periphery of the cover 24 so that access may be had to the combustion zone for removing or repairing the tubes positioned in the combustion zone. A suitable overhead trolley may be provided for supporting a hoisting mechanism for removing the tubes. A plurality of suitably sized openings are provided in the ceramic cover in which cylindrical ceramic mufiles 25 are inserted to retain fuel burners 36 therein for firing the furnace downwardly from the top to provide radiant heat therein. Secondary air for combustion is also supplied through the mufiles 25. As shown in Figure 4, I provide three fuel 4 burners at the top of the combustion chamber which are fired downwardly.

The bottom of the combustion zone is lined with a ceramic or refractory bot-tom cover 35 which is also provided with a suitable number of openings in which ceramic muffles 38 are provided for retaining fuel burners 40 connected to fuel feed lines 40'. I prefer to use adjustable angle burners so that the direction in which the flame is projected can be adjusted. The bottom burners fire the furnace upwardly to provide radiant heat therein. I may also use for certain specific heating operations forced draft burners at the top or bottom, or both at the top and bottom of the furnace. A series of vertically positioned tubes 26 are positioned in the combustion zone adjacent the inner periphery thereof so as to be exposed to the radiant heat supplied by the upper and lower burners. I prefer to provide at least three or more suitably spaced burners at the top and bottom of the furnace, as shown in Figure 4, and to direct the burners so that the flame tends to be projected along the central axis of the cylindrical shell rather than outwardly towards the encircling ring of radiant heat absorption tubes 25. By adjusting the angle of the burners it is obvious that I may exert a more or less effective control over the radiation available to selected segments of the vertically positioned tubes.

Referring to Figures 1 and 4, it will be seen that the vertical series of radiant heat absorbing tubes 28 are arranged closely together in a circle adjacent the inner refractory lining I5. The lower ends of the tubes extend through the bottom ceramic cover 35 and are interconnected at the ends by means of known types of return bends 42 designed to facilitate quick access to the interior of the tubes. The return bends are preferably enclosed in a steel housing 48 which has removable plates 49 for access to the return bends. Ordinarily I provide suitable loose or formed insulation inside the metal housing to minimize radiation of heat from the return bends. The upper ends of the tubes A are connected by suitable return bends 43. The tubes 26 are suitably suspended or supported by hangers 2'! attached to plate 28. The series of interconnected tubes 30 are vertically arranged in the annular convection chamber I8. The upper and lower ends of tubes 39 are interconnected by means of suitable return bends. The tubes 36 are provided with externally extending surfaces or fins 3| which function to absorb the heat from the combustion gases passing upwardly in the convection chamber. The lower ends of the tubes 38' are positioned in ceramic cradles 32 which are supported on plates 33.

The inner refractory wall I1 is provided at its lower end with a plurality of ports or orifices 3'! adjacent the bottom of the convection chamber I8 through which the combustion gases gener ated by the burners pass outwardly. The combustion gases from the top burners 36 pass downwardly in an unobstructed path to the ports 31 and the combustion gases from the bottom burners 40 pass upwardly in an unobstructed path to the ports 37 and then radially outwardly through the ports and into the convection chamber I8, as shown by the arrows in Figure 3. The combustion gases then rise upwardly through the convection chamber i8 flowing over the series of tubes 30 positioned therein which absorb the heat in the combustion gases. The fins 31 on the outer surfaces of the tubes increase the heat absorption. The combustion gases rise to the top of the convection chamber anda-re then directed inwardly in a substantially radial direction in a path between the upper refractory lining 22 and upper cover 23 and then up the stack-4.5 to the atmosphere. The stack is supported by structural members 46., as shown in Figure 1.

I may provide at the top of the convection chamber IS a plurality of individually adjustable plates or dampers 50 which are positioned in the path of the combustion gases flowing radially from top of the convection chamber 13 to the stack 45. The dampers 50 can be turned about their central axes by handles extending outside the furnace so that the dampers 56 can be positioned parallel to the radius passing through their axes or at any angle between this position and a position at 90 therefrom at which the dampers v50 are substantially parallel to the tangent of the circle on which their axes are positioned. It will be understood that these adjustable dampers as extend completely about the circle concentric with the central axis of the convection chamber 18, as shown in Figure 1, and that the multiplicity of plates 51 are arranged so that when they are turned to a position parallel to the tangent of thiscircle, a substantially imperiorate closed wall is interposed in the path of the combustion gases from the convection chamber i8 to the stack 45. As shown in Figure l, a plurality of dampers 50 in the are indicated by letter E in Figure l are positioned to form a closed wall. By adjustment of plates 50 to intermediate position between the closed. position just described and a position parallel to the respective radii, an adjustment of volume of combustion gases passing inwardly to the stack can be made conveniently by appropriate turning of the individual handles 5 i.

11 will now describethe flow of oil within the tube banks. Referring to Figure 4, oil or other fluid is supplied in two separate streams to inlet tubes 55 and 56. The oil supplied to inlet 55 passes serially counter-clockwise through the bank of vertically interconnected tubes in the convection chamber -i-3,.indicated byletter A, and then passes over from tube 51 to tube 58 .in the bank 'of interconnected tubes in the radiant chamber, indicated by letter B, in serially clockwise direction and then passes out of the furnace through outlet tubes 59. The oil supplied to tube 56 passes through the bank of interconnected tubes in the convection chamber 18, indicated by letter 'C, serially in clockwise direc tion, and then passes over from tube 50 to tub 61 in the radiant chamber and through the bank of interconnected tubes in the radiant chamber, indicated by letter D, serially in counter-clockwise direction and out of the furnace through outlet tubeGZ.

While I have chosen to show a heater provided with two parallel passes for the oil flow, it will be understood that a single pass for oil flow or any number of passes may be used as an alternate to the arrangement shown in the drawings.

A modified construction of my furnace is shown in Figures 5 and '6, wherein the upper part of the furnace is provided with a bustle pipe or chamber 65 for collecting the combustion gases leaving the top of the convection chamber. The construction of the parts of the furnace otherwise are the same as shown in Figures 1 to 4 which are indicated by like numerals. The bustle pipeconsists of an outer steel shell '65 which is lined with refractory material 56 and encloses a plurality of ports or openings H5 at the top of the convenetion chamber to permit the combustion gases to pass therethrough. The portion of the vertical supporting beams 8 which pass through these ports are shielded with a jacket of insulation Hi to protect the section of the beams extending through the ports, as shown in Figure 6, against action of the combustion gases. A plurality of individually movable vertical dampers T0 are provided to selectively close the ports. Each of the dampers I0 is suspended on a pair of rods ll which are provided with adjusting handles or wheels 1.2 at their upper extremities for moving the dampers upwardly to partially or completely close the ports FEE as may bedesired. The combustion gases collected in the bustle pipe pass upwardly through the elbow G8 which is connected with the stack 69, as sh wn in Figure 5.

Another modification of my furnace construction is shown in Figures '7 to :11, wherein instead of having the convection chamber concentrio with the combustion chamber, 'a separate vertically positioned cylindrical convection chamber is provided adjacent the combustion chamber and communicating therewith. A re- .niovable bank of vertical interconnected tubes is provided in the convection chamber which communicates with a bank of vertical interconnected tubes in the radiation chamber. Referring to the drawings, the combustion chamber comprises a steel cylindrical shell *8'8 supported by a plurality of vertical I-beam members 82. The shell is lined on its interior with a refractory or insulating'material *8 l. The top of the radiation or combustion chamber is provided with a plurality of burners 34 for firing the chamber downwardly. A plurality of adjustable angle burners 85 'isjprovided at the bottom of the'iurnace for firing the radiation chamber upwardly. The upper end of the cylindrical shelltfl is closed by a steel plate 83 which is lined with refractory material 86. Suitable openings are provided through the top steel plate for insertion of muffles 8'! which retain the burners 84 therein. Upper plates 11 are provided at the top of the shell to form a deck for affording access to the top burners as. The plates vl! are supported by spaced radial beam members l8 connected to a central hub member id, :as shown in Figures 8 and 9.

A bank of vertical interconnected tubes 9b is positioned adjacent the lining 85 in circular formation, as shown in Figure 10.

95. The lower bends 89 are enclosed in a housing as which can be opened vfor providing access to the tubes. The supporting beam members 82 extend above the cylindrical shell 88 and are provided with cross-members 55 which support a circular track 96 adapted to retain a hoist (not shown) for lifting the tubes 9!] when any necessary repairs are to be made.

lhe cylindrical shell 89 is provided with a plurality of ports or openings 91 intermediate its ends to permit the combustion gases to escape. The portion of the supporting Lbeams '82 extending through the ports is protected by an insulatin-g jacket 32. The ports 9'! are enclosed with a steel bustle pipe or chamber 98 lined with refractory or insulating material 99. The ports are adapted to be closed fully or partially as may be desired by means of vertical dampers or plates I carried by rods IOI. The upper ends of the rods are threaded and provided with a surrounding sleeve I02 and a wheel nut I03. Upon rotating the wheel nut I03 the baflle plates can be raised to any desired height to control the size of the port openings, The bustle pipe 98 communicates with the bottom of a cylindrical steel convection chamber I05, as shown in Figure 7. The convection chamber is supported by a plurality of spaced steel I-beam members I06. The shell I05 is lined with a refractory or insulating material I08. The top of the shell communicates with the stack H0. The bottom of the shell I05 is closed by a refractory cover I09 supported on a removable plate I I I. A bank F of vertical interconnected tubes II5 having extending surfaces or fins I I6 is positioned in the convection chamber I05. The bank is connected to an inlet pipe I 2I by means of a removable coupling I and to an outlet pipe I22 by a removable coupling I26. Outlet pipe I 22 is connected to inlet tube I21 of the bank of tubes in the combustion chamber 80. The upper bends N1 of the tubes II5 are connected to cross-members II8 to form an integral bundle of the tubes so that the entire bundle can be lifted by attaching a hoist (not shown) to the eye ring I28. The bank of tubes may be sup-ported directly on the bottom refractory cover I05. For this purpose several of spaced pairs I20 of interconnected tubes may be longer at the bottom than the remaining tubes so as to extend below the bottom of the bank of tubes, as shown in Figure 7. The return bends of the tubes I20 are supported directly on the ceramic cover I09. When it is desired to repair any of the tubes I I5 the connections in tubes I2I and I 22 are broken, and the entire bundle of tubes F is then lifted by attaching a suitable hoisting means to the eye ring I28. The bottom plate II I and its refractory linin I09 are removed. The entire bundle of tubes F can then be lowered and completely removed from the convection chamber I05.

In operation of this furnace construction the combustion gases generated in the furnace or radiation chamber 80 flow in unobstructed opposed directions toward the medial portion of the furnace and escape through the ports 91 into the bustle pipe 98. The combustion gases then pass upwardly through the convection chamber I05 and out through the stack I I0. Oil or other fluid to be heated is fed through the inlet I2I to the bank of tubes H in the convection-chamber and is heated by flowing serially through the bank of tubes I I 5 which absorb heat by convection from the combustion gases flowing upwardly in the convection chamber. The oil then passes out of outlet tube I22 which is connected to the bank of tubes 90 in the radiation chamber 80 where it is heated to the final desired temperature and emerges from outlet tube I25.

My invention is particularly adapted to the use of forced draft burners. In certain combinations of inlet and outlet temperature required for heating the oil and consideration of cost of fuel and other factors, I may provide a fan for impelling combustion air to the burners, in which case I may normally operate the fan so that a slight positive pressure exists throughout the combustion chamber. If the size of the furnace and the cost of fuel make it advisable, I may interpose an air heater between the outlet of the fan and the several burners. I may normally situate this air heater in the path of the combustion gases. For example, I may position the air heater inside stack 45, shown in Figure 2, suitably enlarging the stack to accommodate said air preheater. I may also provide air pre-heating tubes in stack 69, shown in Figure 5. In the event I construct a heater, as shown in Figure 7, I may introduce air pre-heating tubes in the path of the combustion gases either prior to their passage over the bank of tubes F, or I may position the air pre-heating tubes in the space immediately above the bank of tubes F or further up in the stack.

Whereas in the foregoing description I have specifically described a number of modifications embodying my invention all characterized by the positioning of tubes in a radiant heating zone and a convective heating zone, it will be obvious that the cost of the equipment can be reduced at the expense of decreased efllciency of heat utilization by employment of tubes in the radiant zone alone. In such cases the oil or fluid to be heated can be fed directly to the inlet tube of the series of tubes situated in the radiant zone and the combustion gases would pass to the stack without the interposition of any additional oil heating tubes in heat exchange relation with said combustion gases. Under certain circumstances, notably where super-atmospheric oil temperatures are involved, I may also provide passages for combustion air which are in heat exchange but not in material exchange relationship with the flue gases passing from the radiant zone. The combustion air so heated is passed directly to the several burners whereby fuel utilization is improved.

Furnaces constructed in accordance with my invention can be prefabricated in the shop and the separate units assembled on the site where the furnace is to be used. All parts of the furnace are readily accessible so that the tubes can be easily cleaned or repaired whenever necessary. My furnace constructions utilize a minimum quantity of materials, they are relatively light in weight as compared with previous construetions and are structurally strong. Thus erection costs are considerably reduced.

My furnace construction can be operated with maximum thermal efficiency for heating any desired fluids such as liquids, gases, and the like; My furnace construction is particularly adapted for use in the petroleum and chemical industries for distillation, cracking and the heating of various fluids in which substantially uniform heat transfer rates are provided throughout substan* tially the entire length of all the heating elements, both in the radiant and convection zones. A high efficiency of fuel consumption is thus achieved in using my furnace constructions because the full length of all heating tubes is uniformly heated thereby achieving a maximum possible heat transfer rate. My invention thus provides furnace constructions considerably lighter in weight for a given capacity of heat transfer than is possible in prior constructions.

While several embodiments of my invention have been described in detail in the foregoing specification for the purpose of fully disclosing my invention, it is to be understood that my invention is not limited thereto, but includes all changes and modifications which fall within the scope of the appended claims.

I claim:

1. A furnace construction comprising a sub stantially cylindrical combustion chamber, a bank of vertical interconnected tubes positioned adjacent the inner periphery of said combustion 9 chamber, burners at the upper and lower ends of said combustion chamber for heating said combustion chamber, a convection chamber surrounding said combustion chamber, ports in said combustion chamber positioned in the medialzone thereof communicating with said convection chamber to permit combustion gases to pass therethrough into the convection chamber, whereby said combustion gases flow transversely of said vertical tubes, and a bank of vertical interconnected tubes positioned in said convection tioned in the medial zone thereof communicating with said convection chamber to permit combustion gases to pass therethrough into the convection chamber, whereby said combustion gases flow transversely of said vertical tubes, and a bank of vertical interconnected tubes positioned in said convection chamber to absorb heat from the combustion gases passing through said convection chamber and communicating with the bank of tubes in said combustion chamber.

3. A furnace construction comprising a substantially cylindrical combustion chamber, a bank of vertical interconnected tubes positioned adjacent the inner periphery of said combustion chamber, burners at the upper and lower ends of said combustion chamber for providing radiant heat in said combustion chamber, a convection chamber surrounding said combustion chamber,

ports in said combustion chamber intermediate the ends thereof communicating with said convection chamber to permit combustion gases to pass therein, and a bank: of vertically arranged tubes positioned in said convection chamber to absorb heat from combustion gases. passing through said convection chamber and communicating with the bank of tubes in said combustion chamber, a bustle chamber surrounding the upper portion of said convection chamber, said convection chamber being provided with ports. communicating with said bustle chamber to permit the combustion gases to pass therein, and a stack communicating with said bustle chamber.

4. A furnace construction comprising a substantially cylindrical combustion chamber, a bank of vertical interconnected tubes positioned adjacent the inner periphery of said combustion chamber, burners at the upper and lower ends of said combustion chamber for providing radiant heat in said combustion chamber, a convection chamber surrounding said combustion chamber, ports in said combustion chamber intermediate the ends thereof communicating with said convection chamber to permit combustion gases to pass therein, and a bank of vertically arranged tubes positioned in said convection chamber to absorb heat from combustion gases passing through said convection chamber and communicating with the bank of tubes in said combustion chamber, a bustle chamber surrounding the upper portion of said convection chamber, said convection chamber being provided with ports com- 10 municatlng with a bustle chamber to permit the combustion gases to pass therein, dampers for adjustably controlling the opening orsaid ports, and a stack communicating with said bustle chamber.

5. A furnace construction comprising a substantially cylindrical combustion chamber, a refractory lining on the inner periphery of said combustion chamber, a bank of vertical interconnected tubes positioned adjacent saidlining, burners at the upper and lower ends of said combustion chamber for providing radiant heat in said combustion chamber, a substantially cylindrical internal ceramic wall spaced inwardly of said refractory lining forming an annular con vection chamber surrounding said combustion chamber, ports in said internal ceramic wall positioned in the medial zone thereof communicating with said combustion chamber to permit combustion gases to pass therein, whereby said combustion gases flow transversely of said vertical tubes, and a bank of vertical interconnected tubes positioned in said convection chamber to absorb heat from combustion gases passing through said convection chamber and communicating with the bank of tubes in said combustion chamber.

' 6. A furnace construction comprising a substantiaily cylindrical combustion chamber, a bank of vertical interconnected tubes positioned adjacent the inner periphery of said combustion chamber, burners at the upper and lower ends of said combustion chamber for providing radiant heat in said combustion chamber, a convection chamber surrounding the upper portion of said combustion chamber, ports in said combustion chamber positioned in the medial zone thereof communicating with said convection chamber to permit combustion gases to pass therein, whereby said combustion gases flow transversely of said vertical tubes, a bank of vertical interconnected tubes positioned in said convection chamber to absorb heat from combustion gases" passing through said convection chamber and communicating with the bank of tubes in said combustion chamber, the upper portion of said convection chamber communicating with a passageway leading to a stack, and adjustable baflles positioned in said passageway for controlling the flow of combustion gases from said convection chamber to the stack.

7. A furnace construction comprising a substantial-ly cylindrical combustion "chamber, a bank of vertical interconnected tubes adjacent the inner periphery of said combustion chamber, burners at the upper and lower ends of said combustion chamber for providing radiant heat in said combustion chamber, a convection chamber adjacent said combustion chamber, ports in said combustion chamber positioned in the medial zone thereof communicating with said convection chamber to permit combustion gases to pass around a medial portion of the tubes situated in the combustion chamber and into said convection chamber, and a bank of vertical interconnected tubes positioned in said convection chamber to absorb heat from combustion gases passing through said convection chamber and communicating with the bank of tubes in said combustion chamber, the tubes in said convection chamber being movable as a unit from said convection chamber, said convection chamber communicating with a stack to permit the combustion gases to pass to the atmosphere.

8. A furnace construction comprising a substantially cylindrical combustion chamber, a bank of vertical interconnected tubes adjacent the inner periphery of said combustion chamber, burners positioned at the upper and lower ends of said combustion chamber for providing radiant heat in said combustion chamber, a substantially cylindrical convection chamber, adjacent said combustion chamber, ports in said combustion chamber positioned in the medial zone thereof, a bustle chamber surrounding said ports and communicating with-said convection chamber to permit combustion gases to enter said convection chamber and to permit the combustion gases generated in said combustion chamber to pass around a medial portion of the tubes situated in the combustion chamber, and a bank of vertical interconnected tubes positioned in said convection chamber to absorb heat from combustion gases passing through said convection chamber and communicating with the bank of tubes in said combustion chamber, said convection chamber communicating with a stack to permit the combustion gases to pass to the atmosphere.

9. A furnace construction comprising a combustion chamber, burners at the upper and lower ends of said combustion chamber, a bank of vertical interconnected tubes positioned in said combustion chamber for circulating a fluid therein, a convection chamber adjacent said combustion chamber and communicating therewith, said combustion chamber being provided with ports positioned in the medial zone thereof communicating with said convection chamber to permit combustion gases generated in said combustion chamber to pass around a medial portion of the tubes situated in the combustion chamber and into said convection chamber, said convection chamber communicating with a stack to permit the combustion gases to pass to the atmosphere, and a bank of vertical interconnected tubes positioned in said convection chamber and communicating with the bank of tubes in said combustion chamber. 10. A fluid heater construction comprising a combustion chamber having fuel burners at uppar and lower ends and a combustion gas exit orifice positioned in the medial zone in said chamber, a bank of vertical tubes interconnected to form a continuous fluid conduit arranged to intercept energy radiation from combusting fuel in said combustion chamber, intermediate medial portions of said tubes directly athwart'the flow of combustion gas from burners to said exit orifice, a second interconnected bank of tubes forming a fluid conduit in heat exchange relationship with combustion gases enroute from the combustion zone to a stack, said second bank of tubes being shielded from impingement of direct radiation from the combusting fuel, and a connection between the first and second tube banks linking same together to form a continuous conduit for fluid which is to be heated.

11. A fluid heater construction comprising a combustion chamber having fuel burners at-upper and lower ends and a combustion gas exit orifice positioned in the medial zone in said chamber, a bank of vertical tubes interconnected to form a continuous fluid conduit arranged to intercept energy radiation from combusting fuel in said combustion chamber, intermediate medial portions of all of said tubes directly athwart the flow of combustion gas from burners to said exit orifice, adjustable constrictions in the gas exit orifice to control gas flow velocity about selected tubes, a second interconnected bank of tubes forming a fluid conduit in heat exchange relationship with combustion gases enroute from the combustion zone to a stack, said second bank of tubes being shielded from impingement of direct radiation from the combusting fuel, and a connection between the first and second tube banks linking same together to form a continuous conduit for fluid which is tobe heated.

12. A furnace construction comprising a combustion chamber, tubes situated therein and connected together for conducting a fluid in a number of passes encompassing the axis of said chamber and forming a fluid pathway predominantly parallel to said axis, at least one fuel burner at each end of said axis, combustion gas exit positioned in the medial zone in said chamber to withdraw combustion products from the interior volume of the combustion chamber across an intermediate medial portion of each tube in the combustion chamber, a conduit conducting said combustion gas into an adjacent chamber, said chamber being provided with a multiplicity of tubes connected together for conducting a fluid in heat exchange and not in material exchange relationship with the combustion gas, an outlet from the second chamber to a stack for disposition of the combustion gas to the atmosphere and a connection between the tubular aggregate in the second chamber and the tubular aggregate in the combustion chamber to form a continuous channel for fluid flow con tinuously through all tubes in both chambers.

HORACE M. WEIR.

REFERENCES CITED The following references are of record in the file of this patent:

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